Per @blink1037's Sphinx guide at https://github.com/scikit-image/scikit-image/blob/master/doc/README.md my best guess is it has to do with the references in https://github.com/scikit-image/scikit-image/blob/master/skimage/draw/_draw.pyx though none actually appear to be malformatted on a cursory glance.

On Tuesday, December 1, 2015 at 4:18:16 PM UTC-6, Jonathan Helmus wrote:
On 12/01/2015 03:26 PM, Stéfan van der Walt wrote:
> It looks like the docs build is breaking unrelated to #1794:
>
> https://travis-ci.org/scikit-image/scikit-image/jobs/94241837
>
> Any ideas?
>
Sphinx 1.3.2 was released a few days back, could something in this
release have broken the doc build?

    - Jonathan Helmus